1. FIELD OF THE INVENTION
This invention relates in general to a microfiche processing apparatus and in particular to a vesicular film advancing module which co-operates with a basic processing module for processing vesicular microfilm to make duplicates of master microfiche.
2. DESCRIPTION OF THE PRIOR ART
One form of microfilm is microfiche which is generally known as a group of related images arranged on a card-like transparent sheet of film. Typically, these sheets measure 105 mm by 148 mm and are unmounted. The wide-spread use of microfiche has led to a demand for a means of duplicating the microfiche. However, the use of three major types of duplicating film, silver film, diazo film and vesicular film, requires the utilization of three different developing processes with their associated developing apparatus.
The vesicular microfilm generally has a transparent polyester base coated with a layer of thermoplastic resin which includes an ultraviolet sensitive diazonium salt uniformly dispersed within the resin. The film is exposed to a light source through a master microfiche whereupon the salt decomposes in those areas corresponding to the transparent areas of the master microfiche. The decomposing salt releases nitrogen gas so that when the film is heated, the resin will soften to allow the gas to expand to form microscopic vesicules. Since these vesicules are of a different index of refraction than the surrounding resin, they will tend to scatter incident light to form the image. The film is then cooled to prevent excessive growth of the vesicules. Next the film is exposed to ultraviolet light of a high intensity to decompose the previously unexposed salt. The nitrogen gas forms slowly and diffuses to leave clear areas on the film thereby forming a negative of the master microfiche.
Previous vesicular film processors comprised separate machines for exposure and development or a single machine combining both functions. Where separate machines were utilized only one exposure machine and three developers were required to handle the three types of film, but the manual labor involved in transferring the exposed film to the proper developer was costly. Where both functions were combined in the same machine, a substantial investment was required since three different machines were needed to process the three types of film and two exposure machines were included.
An attempt to reduce the previously mentioned costs produced the microfiche duplicator disclosed in U.S. Pat. No. 3,836,252, issued Sept. 17, 1974. This duplicator combined in a single machine one exposure station and separate diazo and vesicular film developing means. However, this machine was limited in flexibility since only two of the three basic types of film could be developed and it was difficult to add means for developing any other type of film. Furthermore, this machine was more expensive than a duplicator for only one type of film where the capability for duplicating the other type of film was not required.
As shown in U.S. Pat. No. 3,775,711, the duplicator defines a generally U shaped path of travel to return the copy sheet adjacent the master microfiche. Since the same light source is utilized for exposing and clearing the film, a mechanical operated reflector must be actuated to illuminate the copy when it is in the clearing area. Cooling air is supplied to the exposure and clearing assembly by a first blower and a pair of hoses connected in parallel and is exhausted by a second blower. Thus, in an attempt to provide a compact duplicator for two different types of microfilm, the complexity of the machine has been increased.